The new season will also tackle the problem of childhood obesity, adding contestants between the ages of 13 and 17 who will compete alongside adult contestants, according to reports. But the teens won't face elimination on the show and will not be weighed for the broadcast.

Michael's long-awaited return comes after the fitness guru announced in December 2010 that the show's 11th season would be her last. At the time, she told fans, "I want to take a year off TV and focus on becoming a mommy and doing more charity work."

On the Today show Tuesday, Michaels told Al Roker she's still adapting to life as a mother. (Watch a clip below.)

"It's been an incredible ride. I'm still adjusting obviously and I don't know that I'll ever fully be adjusted to it, but there's nothing like it," she says. "It brings a whole new level of meaning to your life."

Michaels, who has a tough reputation on The Biggest Loser, admits that going from having no children to being a mom-of-two can be difficult at times.

"I'm not gonna pretend like it's not a challenge," she says. "There are days when I am definitely tearing out my hair."

With her return to television on the horizon and her family supporting her, the trainer couldn't be happier. "Everything you do, you do for them," she says of her children.